Shape Characterization of Fragmented Sand Grains via X-Ray Computed Tomography Imaging

Abstract

The mechanical and hydraulic properties of granular materials are fundamentally affected by the grain size and shape. Three samples of uniformly graded quartz sand with different size ranges were subjected to one-dimensional compression tests up to 40 MPa to fracture the sand into fragments with a variety of sizes and shapes. X-ray computed tomography was used to obtain the morphology of the crushed sand at a resolution of 2.8 μm. A practical divide and stitch method was proposed and implemented to automatically separate and extract individual grains for morphological analysis. This method can reduce the misidentification of grains and voids. Scans of 5,481 grains were used to quantify the three-dimensional morphological properties of grains of different sizes and shapes. The shape descriptors of elongation, flatness, and sphericity were the best way to describe the grain shape. The intermediate Feret diameter was the best parameter for characterizing the grain size. The smaller fragments from the crushed sand were more elongated and had higher flatness and convexity. The distributions of elongation, flatness, sphericity, and convexity for grains in different size ranges followed a normal distribution. The standard deviation in the grain shape descriptors increased for the small grain sizes. The volume and surface area of the grains can be predicted with high confidence using elongation, flatness, and intermediate Feret diameter. Convexity needs to be used along with elongation and flatness to estimate sphericity reliably.